ESTRO 2025 - Abstract Book

S1946

Clinical - Urology

ESTRO 2025

The primary endpoint was investigator-assessed tumour response by PSMA PET before and after SABR. Secondary endpoints included PSMA PET parameters and correlations with tumour pathology, along with tumour size and renal function before and after treatment. Results: Twenty patients with biopsy proven RCC (95% male) with a median age of 80 years (range 51 – 89) were included. Tumour histology: 14 clear cell RCC, 6 papillary RCC, and 1 inconclusive. Median follow-up was 431 days (range, 61 – 1016). Tumour size decreased slightly from a median of 33 mm before SABR to 30 mm at last follow-up. Baseline estimated glomerular filtration rate (eGFR) was 61.0 mL/min/1.73m² (range 23 – 90), with a median decrease of 9.05 mL/min/1.73m² (range 0 – 24) at 6 months post-SABR. PSMA PET scans were performed for 20 tumours before treatment. Four tumours did not show PSMA binding. Of the 16 PSMA-binding tumours, 7 showed no binding at last follow-up, 7 showed reduced binding, and 2 exhibited stable binding. Conclusion: SABR is a safe and effective treatment for patients with inoperable localized RCC. PSMA PET imaging demonstrated changes in PSMA binding after SABR, though the clinical significance of these changes remains unclear. PSMA PET could serve as a potential surrogate imaging marker for treatment response, but further prospective studies are warranted to establish its role and clinical utility. References: 1.Siva S, et al. 5-year outcomes after stereotactic ablative body radiotherapy for primary renal cell carcinomas: an individual patient data meta-analysis from IROCK (the International Radiosurgery Consortium of the Kidney). Lancet Oncol. 2022,23:1508. 2.Siva S, et al. Stereotactic ablative body radiotherapy for primary kidney cancer (TROG 15.03 FASTRACK II): a non randomised phase 2 trial. Lancet Oncol. 2024;25(3):308. 3.Raveenthiran S, et al. The use of (68) Ga-PET/CT PSMA in the staging of primary and suspected recurrent renal cell carcinoma. Eur J Nucl Med Mol Imaging. 2019; 46:2280. 4. Baccala A, et al. Expression of prostate-specific membrane antigen in tumour-associated neovasculature of renal neoplasms. Urology. 2007 ;70(2):385. Keywords: SABR, RCC, PSMA Proffered Paper Focal boost to the intraprostatic tumor for intermediate and high risk prostate cancer: 10-year results of the FLAME-trial Karolina Menne Guricová 1 , Cédric Draulans 2 , Floris J Pos 1 , Linda GW Kerkmeijer 3,4 , Evelyn M Monninkhof 5 , Robert J Smeenk 4 , Martina Kunze-Busch 4 , Johannes CJ de Boer 3 , Jochem RN van der Voort van Zyp 3 , Karin Haustermans 2 , Uulke A van der Heide 1 1 Radiation Oncology, The Netherlands Cancer Institute, Amsterdam, Netherlands. 2 Radiation Oncology, University Hospitals Leuven, Leuven, Belgium. 3 Radiation Oncology, University Medical Center Utrecht, Utrecht, Netherlands. 4 Radiation Oncology, Radboud University Medical Center, Nijmegen, Netherlands. 5 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht, Netherlands Purpose/Objective: The FLAME trial demonstrated that the addition of an isotoxic focal boost to the standard treatment for patients with intermediate- and high-risk prostate cancer increases 5-year biochemical disease-free survival (bDFS) and 1527